This invention concerns the desulfurization of petroleum coke. More particularly, it relates to the treatment of petroleum coke at elevated temperatures and pressures in the presence of hydrogen.
Petroleum coke, as produced from sour crude oils by known and recognized processes, contains sulfur, in various forms, in the range of about 3 to 6 wt.%. Coke used for metallurgical or electrode purposes requires a reduction in the sulfur content, to about 1 to 11/2 wt.%, and a low volatile matter content. This lower sulfur and volatile content coke commands a substantially higher price than ordinary petroleum coke sold for its fuel value. Typically, electrode manufacturers grind and calcine crude petroleum coke to obtain the specifications on sulfur and volatile matter.
Various methods have been used to reduce the sulfur content of petroleum coke. Heating of coke to a temperature of about 2600.degree. F. (1425.degree. C.), to remove a maximum amount of sulfur while it is in an "absorbed" or easily removable form, is one suggested method. Another process uses a plurality of heating zones, with the coke being held at various temperatures for various times. A different process includes the steps of contacting coke with hydrogen at a superatmospheric pressure and at a temperature at which substantial desulfurization occurs, but below the temperature at which substantial volatilization of the charge occurs. Another process desulfurizes coke by the use of hydrogen at relatively low temperatures and at a high pressure. Broadly, the above-described processes involve relatively lengthy residence times, such as from a few minutes to a few hours.